Although our previous studies have suggested the usefulness of KL-6 as a tumor marker [28,29] and a predictor of survival in NSCLC patients treated with EGFR-TKIs [30], significance of circulating KL-6 level as a detector of EGFR-TKIs induced ILD or a predictor of clinical outcome in patients with EGFR-TKIs induced ILD has not been determined yet. Here, EGFR is linked to interstitial lung disease.